No--at least in the U.S., the only thing you'd need permission for would be the names/descriptions of real-life individuals, although this varies a great deal from publisher to publisher (some apparently ask for permissions for use of certain place names, etc--businesses and the like--but this seems ridiculous to me).

If you want, you can run a disclaimer at the end of your story. Like with my stories I write something like "This is a work of fiction and is in no way endorsed by the City of Los Angeles or the Los Angeles Police Department". Although, this looks like an older post, so I'm sure you already wrote it! Hope everything works out for you!